Method of generating power

ABSTRACT

The isomers of dibromotrifluorobenzenes have a boiling point of about 205*C and are useful as working fluids in Rankine-cycle engines. 1,3-Dibromo-2,4,5-trifluorobenzene has a melting point of -41*C and is valuable for use in engines which are exposed to cold weather.

United States Patent echtold et al.

[1 l] Nov. 20, 119/73 METHOD OF GENERATING POWER Inventors: Max F.Bechtold, Kennett Square,

Pa.; Walter Mahler, Wilmington, Del.

E. I. du Pont de Nemours and Company, Wilmington, Del.

Filed: Feb. 29, 1972 Appl. No.: 230,482

Assignee:

US. Cl. 60/36, 252/67 Int. Cl. F01k 25/00 Field of Search 60/36References Cited UNITED STATES PATENTS 6/1962 Tabor et al. 60/36 2/1966Buss et al 60/36 3,282,048 11/1966 Murphy et a1. 60/36 PrimaryExaminer-Martin P. Schwadron Assistant Examiner-Allen M. OstragerAttorneyD. R. J. Boyd 4 Claims, N0 Drawings METHOD OF GENERATING POWERFIELD OF THE INVENTION This invention relates to novel working fluidsfor use in Rankine-cycle engines.

SUMMARY OF THE INVENTION The present invention is a method of generatingpower in which a working fluid is vaporized by heat, the vapor isexpanded to do work in a prime mover and after expansion the vapor iscondensed to a liquid and recycled, in which the working fluid is atleast one isomer of dibromotrifluorobenzene, C I-lBr F preferablyl,3-dibromo-2,4,5-trifluorobenzene and mixtures thereof with otherdibromotrifluorobenzene isomers.

DETAILED DESCRIPTION OF THE INVENTION Recently there has beenconsiderable interest in external combustion engines, particularly thoseworking on the Rankine cycle for use in relatively low power, portableengines such as car or light boat engines. The fuel requirements forsuch engines are relatively uncritical. Further, the fuel is burnedcontinously and the heating means can be readily designed to minimizeair pollutants in the combustion product.

Water has long been used as the working fluid for Rankine-cycle enginessuch as reciprocating engines and turbines. Water has the disadvantagesof requiring high temperatures and pressures to obtain usefulefficiency. Very high velocities are obtained on expansion in simplenozzles so that high speed multiple stage turbines are required togenerate power efficiently.

It has been recognized that high density working substances operating atsubcritical temperatures and pressures avoid many of the disadvantagesof water. Relatively low temperatures and pressures are required,condensation can be effected with relatively small aircooled condensers,and relatively low efflux velocities are obtained which make feasiblethe use of singlestage turbine prime movers operating at relatively slowspeeds. In addition to possessing suitable thermodynamic properties foruse in Rankine-cycle engines, the power fluid must also have sufficientthermal stability. Further it is desirable that the toxicity should below and that the substance should not support combustion in case ofaccidental rupture of the closed system containing the working fluid.Again, for use in portable engines such as automobile engines, it isdesirable that the fluid does not freeze under winter conditions, i.e.,preferably that the freezing point should be below 40C.

Efficient turbine engines have been designed using a rotary boiler andcondenser wherein the power fluid is pumped from the condenser to boilerby centrifugal force as described in the following patents andapplications of William A. Doerner: U. S. Pat. Nos. 3,590,786; 3,613,368and patent application Ser. No. 110,478, filed Jan. 28, 1971. For use insuch engines, it is desirable that the fluid have a high density.

It has now been discovered that the isomers of dibromotrifluorobenzenemeet the above criteria, except for the very low freezing point. Theboiling point of the isomers is about 205C in each case, and the thermalstability is surprisingly good at 350C in contact with steel, stainlesssteel or aluminum. in particular, the l,3-dibromo-2,4,5-trifluorobenzenehas a freezing point of 4lC and is suitable for use in externalcombustion engines which are exposed to winter conditions.

All of the isomers give thermal efficiencies in the Rankine cycle ofabout 20 percent at practical temperatures for boiler and condenser.

The 1,3-dibromo-2,4,6trifluorobenzene isomer has been reported by G. G.Yakobson, N. E. Miranova, A. K. Petrov and N. N. Vorozhtov, Jr., ZhurnalObshchei Khimii 36, 147 (1966) to have been isolated from the reactionproduct of C Br with KF. This isomer is better prepared by the followingprocedure:

g. of 1,3,5-trifluorobenzene are placed in a 250 cc 3-necked flaskfitted with a condenser and dropping funnel, and 0.1 g. of iron powderis added as a catalyst. g of bromine is then added dropwise over a 3hour period from the dropping funnel while stirring the contents of theflask with a magnetic stirring bar. An additional 60 g of bromine isthen added over a 4 hour period. The product is l,3-dibromo-2,4,6-trifluorobenzene, the remainder being isomers of C H BrF The product isworked with water, dried with CaSO.,, and distilled at 25 mm pressureand 101C to give 60 g of product with normal b.p. 205C and m.p. +30C asdetermined by differential thermal analysis. The identity is confirmedby F nmr.

The other isomers can be prepared by similar methods as a mixture, whichcan be separated into the individual components by gas chromatography:

25 g of 1,2,4-trifluorobenzene and 0.1 g of aluminum powder are placedin a 250 cc 3-necked flask fitted with a condenser, a dropping funneland a magnetic stirring bar. Over a 2 hour period is added 31 g ofbromine. Reaction is indicated by the steady elimination of HBr. Afurther 31 g of bromine is then added followed by 0.1 g of aluminumtrichloride, and the reaction mixture is stirred overnight. After 16hours the product is washed with water, dried over calcium sulfate anddistilled under vacuum. A fraction weighing 7 g and boiling at 94C, 20mm is found to have the composition C HBr F and to melt between 26C and39C. The mixture is separated into l,3-dibromo-2,4,5- trifluorobenzene,m.p. +4lC and l,2-dibromo-3,4,6- trifluorobenzene, m.p. +19C by gaschromatography.

Since obvious modifications and equivalents in the invention will beevident to those skilled in the arts, we propose to be bound solely bythe appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of generating power by heating and vaporizing a workingsubstance, expanding the vapor of said working substance in a primemover to do work, and after doing said work condensing said vapor andrecycling wherein said working substance is at least onedibromotrifluorobenzene isomer.

2. Method of claim 11 in which said working substance comprisesl,3-dibromo-2,4,5-trifluorobenzene.

3. The method of claim I wherein the working substance is subjected tocentrifugal force during the steps of heating and condensing and isrecycled by centrifugal force.

4. The method of claim 2 wherein the working substance is subjected tocentrifugal force during the steps of heating and condensing and isrecycled by centrifugal force.

2. Method of claim 1 in which said working substance comprises 1,3-dibromo-2,4,5-trifluorobenzene.
 3. The method of claim 1 wherein the working substance is subjected to centrifugal force during the steps of heating and condensing and is recycled by centrifugal force.
 4. The method of claim 2 wherein the working substance is subjected to centrifugal force during the steps of heating and condensing and is recycled by centrifugal force. 